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76105DK8 Datasheet PDF : 12 Pages
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HUF76105DK8
Thermal resistances corresponding to other copper areas
can be obtained from Figure 23 or by calculation using
Equation 2. RθJA is defined as the natural log of the area
times a coefficient added to a constant. The area, in square
inches is the top copper area including the gate and source
pads.
RθJA = 103.2 – 24.3 × ln (Area)
(EQ. 2)
300
RθJA = 103.2 - 24.3 * ln(AREA)
250
228 oC/W - 0.006in2
200
191 oC/W - 0.027in2
150
100
50
Rθβ = 46.4 - 21.7 * ln(AREA)
0
0.001
0.01
0.1
1
AREA, TOP COPPER AREA (in2) PER DIE
FIGURE 23. THERMAL RESISTANCE vs MOUNTING PAD AREA
While Equation 2 describes the thermal resistance of a
single die, several of the new UltraFETs are offered with two
die in the SOP-8 package. The dual die SOP-8 package
introduces an additional thermal component, thermal
coupling resistance, Rθβ. Equation 3 describes Rθβ as a
function of the top copper mounting pad area.
Rθβ = 46.4 – 21.7 × ln (Area)
(EQ. 3)
The thermal coupling resistance vs. copper area is also
graphically depicted in Figure 23. It is important to note the
thermal resistance (RθJA) and thermal coupling resistance
(Rθβ) are equivalent for both die. For example at 0.1 square
inches of copper:
RθJA1 = RθJA2 = 159oC/W
Rθβ1 = Rθβ2 = 97oC/W
TJ1 and TJ2 define the junction temperature of the respective
die. Similarly, P1 and P2 define the power dissipated in each
die. The steady state junction temperature can be calculated
using Equation 4 for die 1and Equation 5 for die 2.
Example: Use Equation 4 to calculate TJ1 and Equation 5 to
calculate TJ2 with the following conditions. Die 2 is
dissipating 0.5 Watts; die 1 is dissipating 0 Watts; the
ambient temperature is 70oC; the package is mounted to a
top copper area of 0.1 square inches per die.
TJ1 = P1RθJA + P2Rθβ + TA
(EQ. 4)
TJ1 = (0 Watts)(159oC/W) + (0.5 Watts)(97oC/W) + 70oC
TJ1 = 119oC
TJ2 = P2RθJA + P1Rθβ + TA
(EQ. 5)
TJ2 = (0.5 Watts)(159oC/W) + (0 Watts)(97oC/W) + 70oC
TJ2 = 150oC
The transient thermal impedance (ZθJA) is also effected by
varied top copper board area. Figure 24 shows the effect of
copper pad area on single pulse transient thermal
impedance. Each trace represents a copper pad area in
square inches corresponding to the descending list in the
graph. SPICE and SABER thermal models are provided for
each of the listed pad areas.
Copper pad area has no perceivable effect on transient
thermal impedance for pulse widths less than 100ms. For
pulse widths less than 100ms the transient thermal
impedance is determined by the die and package. Therefore,
CTHERM1 through CTHERM5 and RTHERM1 through
RTHERM5 remain constant for each of the thermal models. A
listing of the model component values is available in Table 1.
160 COPPER BOARD AREA - DESCENDING ORDER
0.020 in2
0.140 in2
120 0.257 in2
0.380 in2
0.493 in2
80
40
0
10-1
100
101
102
103
t, RECTANGULAR PULSE DURATION (s)
FIGURE 24. THERMAL RESISTANCE vs MOUNTING PAD AREA
8
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